What is an ocean tide? An ocean tide is the name given to the rise and fall on the level of the sea water in respect to land. These tides occur in a cycle due to changes in the gravitational pulls between the Earth, the moon, and even the Sun. Those changes occur in relationship to the locations the objects named above have in comparison to each other. One of the main things that set the tide cycle is the Earth-Moon rotational/revolutionary relationship.
A tidal period is set according to the lunar day. That makes it 24 hrs and 50 minutes long cycle, due to the fact that the Moon is not a stationary object. That means that it takes the Earth that exact amount of time to catch back up with the Moon. [1]
provided by NOAA's National Ocean Services
Gravity and Influential Forces
“Gravity is the force exerted by an object with a mass on another object with mass”. Gravity influences the way many things function whether it be within the planet, its satellite, or the entire planetary system. That difference is known as the tidal force. Explaining what tides are and how they function is a fairly easy process. Tides occur because there is a constant gravitational pull between the Moon and the Earth and the Sun and Earth. The power in which the Sun pulls on the Earth is extremely small in comparison to the strength in which the Moon pulls. The strength in which the Moon is able to pull on the Earth differs depending on what point of the Earth it’s located. “The side of the Earth facing the Moon is about 6400 Kilometers closer to the Moon than the center”. Because there is less distance between the Moon and the surface of the Earth facing the Moon, its gravity is able to pull stronger, creating a tidal bulge. A tidal bulge is “the elongation of the Earth due to the difference of the gravitational force on the side closest to the Moon and that of the side farthest. The long axis of such bulge points toward the Moon”. Ocean tides are one of those things that occur due and in relation to the gravitational forces the Earth relates to the Moon and Sun and vice versa, as well as the outcome of the difference between them. Depending on where an area is located compared to the bulge determines what type of tide will be experienced.
There are 5 terms often used to refer to the type of tide: neap, spring, semi-diurnal, diurnal, and mixed semi-diurnal. Each happens at a specific time of the Moon cycle, and at a specific area of the Earth.
Neap Tides
Neap tides for instance occur twice a month. That is in the first and the third quarters of the Moon. This is when the pull of the Sun is happening at a right angle to the pull of the moon on the Earth. The counteraction between the forces in the Earth causes the strength of the pull to be lower. Since the force is smaller the water level in the “low” tide does not differ much from that of the “high” tide. As a matter of fact the levels are very closed to leveled. This in turn is considered a weak tide.
animation courtesy of http://home.hiwaay.net/~krcool/Astro/moon/moontides/
Spring Tides
Then there are the spring tides. These tides occur during either a full moon or a new moon. They are very strong tides, due to the fact that the Earth, the Moon, and the Sun are all a lined. Thanks to the fact that there are no counteractions between the bodies there is a strong force acting together. Since the force is large, it causes a large difference among the levels of water. The “high” tide is a very high tide, and the “low” tide is very low.
Semi-Diurnal Tides
There are also the tides that are known as Semi-diurnal. This is more of a description of a type of cycle, than the tide itself. Semi-diurnal means twice a day. So when referring to tide cycles, it states that during a day two complete tidal cycles will be experienced. There will be two times in which there will be a high tide. They are approximately the same height. Then, there will also be two times in which a low tide be experienced. Here, they will also be very close in size.
Image courtesy of NOAA's National Ocean Services
Diurnal Tides
Now, there is also a name to having only one tide cycle per day. That is called Diurnal. Instead of there being two high and two low tides, there is only one of each. (Net Industries)
Image courtesy of NOAA's Nationaly Ocean Services
Mixed Semi-Diurnal
There are however places that experience a cycle very similar to that of the Semi-diurnal. These areas are said to have Mixed Semi-diurnal cycles. The difference between this cycle and that mentioned above is that there is a difference in heights between the two high tides, as well as a difference between the two low tides. (Glendale City College).
Image Courtesy of NOAA's National Ocean Services
Ways of Measurement
Having so many different types of tides as well as cycles doesn’t mean that they cannot be measured pretty accurately. Measuring the water level in the past was first done using a “recorder that was driven by a float in a “stilling” well.” “The point of using a stilling well was that it calms the waters around the sensor. The usual well was made of a 12 in wide pipe. Inside the well, an 8 in diameter float is hung by a wire from the recorder which lies above". Also, before the use of computers was started, the data was recorded on a continuously running pen and ink strip chart. These charts were collected once a month and manually processed. As the years went by, tide houses were built. This helped to protect the water level recorders from harsh environmental conditions. Data was started to be recorded at 6 minute intervals making the measurements more reliable. As computers were starting to be introduced a "mechanical 'punch' recorder" was also brought in to analyze the tidal patterns. Even though the forms of obtaining and recording data had become better equipped, there was still room for further development.
Images courtesy of NOAA's National Ocean Services
Now technology has cut down on the problems that were seen by the old tidal recorders. To improve measurement accuracy, as well as customized data collection, microprocessor-based technologies were introduced. Floats were also substituted with the use of acoustics and electronics. The new recorders send an audio signal down a sounding tube and measure how long it takes for the signal to bounce back from the water surface. Also, a satellite is used to control the time intervals on which the recorders take a reading.
Being able to quickly and accurately obtain information regarding the tides is very helpful especially during storms. The use of technology allows for quicker distribution and clearer analyzing of not only the heights of the tide, but also of wind speeds and directions, water current speed and direction, air and water temperature, and barometric pressure. That is vital information in case of an oceanic emergency. (NOAA).
Ocean Tides
Table of Contents
These tides occur in a cycle due to changes in the gravitational pulls between the Earth, the moon,
and even the Sun. Those changes occur in relationship to the locations the objects named above have in comparison to each other. One of the main things that set the tide cycle is the Earth-Moon rotational/revolutionary relationship.
Quick Run
Ocean Tides on Prezi
Lunar Days
A tidal period is set according to the lunar day. That makes it 24 hrs and 50 minutes long cycle, due to the fact that the Moon is not a stationary object. That means that it takes the Earth that exact amount of time to catch back up with the Moon. [1]
Gravity and Influential Forces
“Gravity is the force exerted by an object with a mass on another object with mass”. Gravity influences the way many things function whether it be within the planet, its satellite, or the entire planetary system. That difference is known as the tidal force. Explaining what tides are and how they function is a fairly easy process. Tides occur because there is a constant gravitational pull between the Moon and the Earth and the Sun and Earth. The power in which the Sun pulls on the Earth is extremely small in comparison to the strength in which the Moon pulls. The strength in which the Moon is able to pull on the Earth differs depending on what point of the Earth it’s located. “The side of the Earth facing the Moon is about 6400 Kilometers closer to the Moon than the center”. Because there is less distance between the Moon and the surface of the Earth facing the Moon, its gravity is able to pull stronger, creating a tidal bulge. A tidal bulge is “the elongation of the Earth due to the difference of the gravitational force on the side closest to the Moon and that of the side farthest. The long axis of such bulge points toward the Moon”. Ocean tides are one of those things that occur due and in relation to the gravitational forces the Earth relates to the Moon and Sun and vice versa, as well as the outcome of the difference between them. Depending on where an area is located compared to the bulge determines what type of tide will be experienced.
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http://video.foxnews.com/v/4485138/billboards-provoking-the-faithful-/Types of tides
There are 5 terms often used to refer to the type of tide: neap, spring, semi-diurnal, diurnal, and mixed semi-diurnal. Each happens at a specific time of the Moon cycle, and at a specific area of the Earth.
Neap Tides
Neap tides for instance occur twice a month. That is in the first and the third quarters of the Moon. This is when the pull of the Sun is happening at a right angle to the pull of the moon on the Earth. The counteraction between the forces in the Earth causes the strength of the pull to be lower. Since the force is smaller the water level in the “low” tide does not differ much from that of the “high” tide. As a matter of fact the levels are very closed to leveled. This in turn is considered a weak tide.
Spring Tides
Then there are the spring tides. These tides occur during either a full moon or a new moon. They are very strong tides, due to the fact that the Earth, the Moon, and the Sun are all a lined. Thanks to the fact that there are no counteractions between the bodies there is a strong force acting together. Since the force is large, it causes a large difference among the levels of water. The “high” tide is a very high tide, and the “low” tide is very low.
Semi-Diurnal Tides
There are also the tides that are known as Semi-diurnal. This is more of a description of a type of cycle, than the tide itself. Semi-diurnal means twice a day. So when referring to tide cycles, it states that during a day two complete tidal cycles will be experienced. There will be two times in which there will be a high tide. They are approximately the same height. Then, there will also be two times in which a low tide be experienced. Here, they will also be very close in size.
Diurnal Tides
Now, there is also a name to having only one tide cycle per day. That is called Diurnal. Instead of there being two high and two low tides, there is only one of each. (Net Industries)
Mixed Semi-Diurnal
There are however places that experience a cycle very similar to that of the Semi-diurnal. These areas are said to have Mixed Semi-diurnal cycles. The difference between this cycle and that mentioned above is that there is a difference in heights between the two high tides, as well as a difference between the two low tides. (Glendale City College).
Ways of Measurement
Having so many different types of tides as well as cycles doesn’t mean that they cannot be measured pretty accurately. Measuring the water level in the past was first done using a “recorder that was driven by a float in a “stilling” well.” “The point of using a stilling well was that it calms the waters around the sensor. The usual well was made of a 12 in wide pipe. Inside the well, an 8 in diameter float is hung by a wire from the recorder which lies above". Also, before the use of computers was started, the data was recorded on a continuously running pen and ink strip chart. These charts were collected once a month and manually processed. As the years went by, tide houses were built. This helped to protect the water level recorders from harsh environmental conditions. Data was started to be recorded at 6 minute intervals making the measurements more reliable. As computers were starting to be introduced a "mechanical 'punch' recorder" was also brought in to analyze the tidal patterns. Even though the forms of obtaining and recording data had become better equipped, there was still room for further development.
Images courtesy of NOAA's National Ocean Services
Now technology has cut down on the problems that were seen by the old tidal recorders. To improve measurement accuracy, as well as customized data collection, microprocessor-based technologies were introduced. Floats were also substituted with the use of acoustics and electronics. The new recorders send an audio signal down a sounding tube and measure how long it takes for the signal to bounce back from the water surface. Also, a satellite is used to control the time intervals on which the recorders take a reading.
Being able to quickly and accurately obtain information regarding the tides is very helpful especially during storms. The use of technology allows for quicker distribution and clearer analyzing of not only the heights of the tide, but also of wind speeds and directions, water current speed and direction, air and water temperature, and barometric pressure. That is vital information in case of an oceanic emergency. (NOAA).